From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
The low-speed heating, output performance, and commutation tests comparing two different electrical machines.
| Identifier | ExFiles\Box 168a\3\ img426 | |
| Date | 7th September 1937 | |
| -2- Low-speed heating test. In this test, the extent to which a machine heats up on load, and its maximum output, are ascertained by finding the maximum current at 13 volts, and lowest speed that will produce a steady temperature rise above ambient temperature, of 44 to 46 centigrade degrees. Results obtained were:- | | Amperes at 13 volts | Speed in R.P.M. | |---|---|---| | Lucas. | 23.0 | 1,750 | | A.R. | 21.0 | 1,350 | The higher output from the Lucas machine, is due to the fact that it occurs at a higher speed, when the cooling effect of the fan is greater. In any case, we have an excess of available output, as, from commutation point of view, we cannot at present really cope with more than about 18 amperes. Output performance. The output of a dynamo, is taken to be that output that the machine will deliver to a chassis system, the voltage of which is 13.0 volts; with the machine at maximum under-bonnet temperature. The variation in this output with speed, is expressed in a characteristic curve. Attached is a sheet showing this curve for each machine, from which it can be seen that the Lucas machine has a lower cutting-in speed. The difference in cutting-in speed, represents a sacrifice made on the part of the A.R. dynamo, for the sake of quietness. Apart from this, the two curves are very similar, the Lucas machine rising less rapidly, and falling behind at the higher speeds. Commutation and noise. The worst conditions of running are those of high-speed travelling at night, i.e. combined high dynamo speed and heavy load. This causes sparking at the bushes, which in turn wears away both commutator and brushes. Sparking thus limits the time a machine can be run before | ||